Temporal variability of bedload vs suspended sediment load and respective hysteresis cycles in a glacier-fed Alpine river

Sediment transport is a fundamental process in shaping streams and rivers morphology and influencing aquatic ecosystems. Understanding its dynamics and rates is crucial for ecologists, as it affects aquatic habitats, helps mitigate natural hazards, and support reservoirs management to prevent siltation. This study investigates the relationship between water discharge, suspended sediment, and bedload discharge in the glacier-fed Sulden/Solda River (Eastern Italian Alps, drainage area 130 km2). Data were collected from 2014 to 2020 using a turbidimeter for suspended sediment and eight geophone plates for bedload discharge. Results indicate that suspended load accounts for 93.5% of the total sediment discharge, while bedload represented the rest. Hysteresis cycles analysis reveals that both suspended sediment and bedload discharge predominantly follow complex clockwise patterns. Specifically, 46.0% of suspended sediment and 59.2% of bedload discharge cycles exhibit complex hourly patterns, while 18.9% and 7.9%, respectively, display simple clockwise cycles. Less than 35.0% of cycles for both fractions are counterclockwise (either complex or simple). The type of hysteresis appears unrelated to water discharge. Additionally, as water discharge increases, both suspended and bedload discharges rise, but bedload discharge is proportionally higher during low water discharge, especially at the end of the ablation season. These findings indicate that sediment transport in this glacial basin is predominately in suspension, with high sediment availability and strong connectivity within the channel network.